The present invention relates to a method of deriving a quantitative measure of a degree of calcification of an aorta.
Inpainting is a technique that originates from retouching paintings where one wants to recreate lost or damaged structures in a legible way. Digital inpainting uses spatial or frequency information to restore partially damaged/removed images.
Various inpainting techniques are known that enable image restoration, in particular for photographs, videos and films.
It is known to detect and inpaint small regions in mammograms that possibly define a micro calcification to enable detection of calcified regions. Subsequently, features such as the average and the standard deviation of intensity values are extracted from both the pre- and the post-inpainting regions. A classifier is trained to distinguish between true micro calcifications and false positives based on the extracted features. The comparison between a region and its inpainting is used to enable detection. Thus a binary decision of whether a region is abnormal, i.e. different from its surroundings, is made.
There are, however, no methods available at present that use inpainting to give more than a basic indication of the presence of a calcification. In the present invention, it has been realised that such a method may be useful in the diagnosis of various diseases, for example, atherosclerosis.
Atherosclerosis is a process in which deposits of fatty substances, cholesterol, cellular waste products, calcium and other products build up in the inner lining of an artery.
Previous known methods of assessing atherosclerotic plaque include the assessment of the calcification index on lateral 2-D x-rays. In this method, aortic calcification is assessed at each vertebral segment. Calcific deposits are regarded as present if the densities are visible in an area parallel to the lumbar spine and anterior to the lower part of the spine. As the abdominal aorta in the L1-L4 region of the spine is occasionally situated lateral to the spine, aortic densities of the lumbar region can sometimes overlap the vertebrae. Densities overlapping the vertebrae are scored present only if they extend from or form a clear pattern with those of the lower part of the aorta. Calcific deposits in the abdominal aorta adjacent to each lumbar vertebra are assessed separately for the posterior and anterior wall of the aorta using the midpoint of the intervertebral space above and below the vertebrae as boundaries.
The lesions are graded according to specific categories: Lesions with small scattered deposits that extend along less than ⅓ of the longitudinal wall of the aorta; lesions where ⅓ or more, but less than ⅔ of the longitudinal wall is calcified and lesions where ⅔ or more of the longitudinal wall is calcified.